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"  A dangerously cold Arctic air mass is ravaging the Midwest, ushering in the coldest temperatures seen in 20 years. The so-called &amp;quot;polar vortex&amp;quot; is shutting down schools in Minnesota, grounding thousands of flights, and prompting Indiana to declare a state of emergency in 25 counties. On Monday the National Weather Service observed wind gusts as high as 60 miles per hour in Buffalo, New York, while parts of Montana felt winds as cold as -60F. And it&amp;#039;s not over yet, says the National Weather Service: &amp;quot;The bitter cold that spread over the central U.S. this weekend will usher into the eastern third of the Nation&amp;quot; on Tuesday. So what exactly is a polar vortex? Basically it&amp;#039;s a frigid cyclone. These big swirling air masses normally hover over the North and South poles in the wintertime. In the Northern hemisphere, polar vortices center around northeastern Siberia and Baffin Island in Canada, where winds spin counter-clockwise around a low-pressure center at speeds of up to 100 miles per hour. The current outbreak is believed to have formed over Siberia.  Normally a polar vortex traps cold air in the Arctic, but every now and then it dips down into southern Canada. On rarer occasions, the entire polar vortex can be pushed even further south by uncommon weather patterns, or a piece of it can break off and get flung south. That&amp;#039;s what&amp;#039;s happening in this case, says meteorologist Jon Erdman at Wundergound.com. &amp;quot;[A] large piece of the vortex broke off and was forced well to the south over Ontario and the northern Great Lakes.&amp;quot; A northward diversion of the polar jetstream over the West Coast is helping to push the system southward, Erdman writes.   Some evidence suggests that global warming may be contributing to such polar spillovers, as warmer than normal temperatures in the Arctic weaken air circulation in the vortex and make it easier to break apart.  In January 1985, a southward shift of the polar vortex killed 126 people, destroyed 90 percent of Florida&amp;#039;s citrus crop, and set record-lows across the East Coast. As a result, January 21,1985 is considered the coldest day of the twentieth century.  Meteorologists are suggesting that the worst of this year&amp;#039;s polar outbreak will blow over by Thursday.   "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/science/environment/a9897/the-science-behind-the-polar-vortex-16352023/>